Real-time transmission protocol RTP provides data with a terminal transmitted to terminal delivery services such as interactive video audio or simulation data under multicast or unicast network services. The application executes RTP on the UDP to use its multi-channel technology and inspection and services; there is also a protocol donation part of the transfer protocol function. However, RTP can be used together with other suitable underlying networks or transport protocols. If the underlying network provides multicast allocation, RTP can use the multicast allocation to support data transfer of multiple target files.
RTP itself does not provide any mechanism or other quality service QoS guarantee for timely delivery, but it relies on low-level services to achieve this process. RTP does not guarantee the transfer process or prevent disorderly transmission, and cannot determine the reliability of the underlying network. RTP is in orderly, the serial number in the RTP allows the receiver to reconstruct the sender's package sequence, and the serial number can also be used to determine the appropriate packet position, such as in video decoding, no need to decode.
RTP consists of two similar links:
RTP: Transmits data with real-time properties; RTP control protocol RTCP: Monitor service quality and transmits information on the ongoing session participants. The second aspect of the RTCP applies to loose controlled sessions is sufficient, that is, without clear control members and organizations, it is not used to support all control communication requests for an application.
Protocol structure
1238916bitvpxcsrc Count MPAYLOAD TYPESEQUENCE NUMBERTIMESTAMPSSRCCSRC (Variable 0 - 15 Items 32Bits EACH)
V - version. Identify the RTP version. P - gaps. When set, the data packet contains one or more additional gap positions, where this part is not a payload. X - extension. When setting, after the fixed head, set an expanded head according to the specified format. CSRC Count - includes the number of CSRC identifiers (after the fixed head). M - tag. The interpretation of the tag is defined by the Profile file. Allow important events such as frame boundaries to mark in the packet stream. PayLoad Type - Identify the format of the RTP payload and determine it through the application. The Profile file specifies the default static mapping encoded from the PayLoad to the PayLoad format. Another PAYLOAD TYPE encoding may be dynamically defined by non-RTP methods. Sequence Number - An RTP packet is sent, and the serial number adds 1. The recipient can sequentially detect the loss of the packet and restore the data package sequence. TimeStamp - Reflects the sampling time of the first eight-bit group in the RTP packet. Sampling time must provide linear non-change incremental acquisition through clock to support synchronous and jitter calculations. SSRC - Synchronous source. This identifier is a random selection, which is intended to ensure that there is no two synchronization sources having the same SSRC identifier in the same RTP session. CSRC - Contribute source identifier. Identify the contribution of payload in the packet.
Related protocols RTCP, RTSP, UDP, TCP, IP organization Source RTP is defined in RFC 3550 and 3551 by IETF (www.ietf.org). Related Links http://www.javvin.com/protocol/rfc3550.pdf: RTP: A Transport Protocol for Real-Time Applicationshttp: //www.javvin.com/protocol/rfc3551.pdf: RTP Profile for Audio and Video Conferences With minimal control
